Description of the Related Art
The present invention relates to an arrangement for transporting air with the aid of a so-called ion wind or corona wind and being of the kind set forth in the pre-characterizing clause of claim 1.
It is known that air can be transported, in principle, with the aid of a so-called electric ion-wind or corona-wind. An ion wind is created when a corona electrode and a target electrode are mutually spaced apart and connected to a respective terminal of a d.c. voltage source, and when the construction of the corona electrode and the voltage of the d.c. voltage source are such as to give rise to a corona discharge at the corona electrode. This corona discharge, in turn, gives rise to air ions of the same polarity as the polarity of the corona electrode, and possibly also to electrically charged aerosols, i.e. air suspension of solid particles or liquid droplets which are charged electrically as a result of collision with the electrically charged air ions. The air ions migrate rapidly, under the influence of the electric field, from the corona electrode to the target electrode, where they relinquish their electric charge and return to electrically neutral air molecules. During their movement between the electrodes, the air ions constantly collide with the electrically neutral air molecules, thereby transferring electrostatic forces thereto, so that said air molecules are also drawn in a direction from the corona electrode towards the target electrode, thereby effecting transportation of air in the form of a so-called ion wind, or corona wind.
Earlier proposed air transporting arrangements based on the electric ion-wind concept are found described, for example, in DE-OS 2854716, DE-OS 2538959, GB-A-2112582, EP-A1-29421 and US 4,380,720. These earlier proposed arrangements, however, have been shown to be highly ineffective and have not obtained any practical significance. Air transporting arrangements which are based on the ion wind concept and which display marked improvements over the earlier proposed arrangements, both in regard to efficiency and to practical utility, are described in our contemporary international patent application PCT/SE85/00538.
A common feature of all of the aforesaid arrangements is that a corona electrode and a target electrode are arranged spaced from one another in the desired direction of air flow, the corona electrode and the target electrode both being constructed so that air can pass therethrough. The target electrode is placed downstream of the corona electrode, as seen in the direction of air flow, and a source of d.c. voltage is connected between the corona and target electrodes, the voltage of the d.c. voltage source and the construction of the corona electrode being such as to create at the corona electrode a corona discharge which will produce air ions. In all of the aforementioned cases the electrodes are arranged within the confines of an airflow duct, although when such an arrangement is constructed in accordance with our aforesaid international application the provision of such a duct is not an unavoidable necessity, as is made clear in the aforesaid international application.
The corona electrodes hitherto proposed for use with air transporting arrangements of this kind can be divided into two main categories, namely a first category in which the corona electrode comprises an elongated, substantially wire-like corona element which is intended to extend across the airflow path, and a second category in which the corona electrode comprises pointed corona elements, for example corona elements in the form of short, thin wires or needle-like devices which extend axially in the airflow path, with one end of the element secured in a holder and the other, pointed end, which is unattached, being directed towards the target electrode.
One requirement placed on the corona electrode of an air transporting arrangement of the kind in question is that the corona discharge created at said electrode gives rise to the greatest possible transportation of air. Another requirement is that the corona discharge is stable and creates but the smallest possible amount of toxic gases, primarily ozone and oxides of nitrogen.